1. Field of the Invention
The invention relates to a method to secure the operations for accessing detachable cards for computers. It can be applied to mass storage cards for microcomputers or personal computers (PCs) and to cards having an input/output function. It can be applied especially to cards meeting the PCMCIA standard.
2. Description of the Prior Art
Mass-storage-cards, which are sometimes also called PC cards, comprise several memory chips and a connector (a 68-pin female connector according to the PCMCIA standard of the Personal Computer Memory Card International Association, 1030B East Duane Avenue, Sunnyvale, Calif.). The card can be plugged into a corresponding (male) connector of the computer. The connections are such that the memory can be addressed by a parallel input-output port of the PC, either as if the memory were a magnetic mass storage memory or as if it were an extension of the random-access memory of the computer.
Apart from mass storage cards, there also exist cards for personal computers that have the functions of communication between the computer and the exterior, and therefore comprise not only a connector designed to provide the link with the personal computer but also means of connection with the exterior. These cards are called input/output function cards, or I/O function cards. The typical example of a card with a communications function is the modem which is connected by a first connector to the computer and by a second connector to a telephone line for the sending of digital data elements on the line. Another example of a card with a communications function is a card for local area networks where communications with the exterior are carried out not by a connector with physical contacts but by RF transmission in a close environment.
The existing communications cards generally use the RS232C output of the computers which delivers digital data in serial form, well suited to communication by modem or by radio. Or, again, the cards are directly mounted inside the computer and do not take the form of plug-in cards.
There furthermore exist communication cards that can be plugged into the memory extension connector provided in many computers. This connection is made without there appearing any problem of communications protocol. The description of such a card will be found in the French patent application No. 92 08554 published under No. 2 693 575.
The technical problem that the applicant has sought to resolve is that of protecting the operations of accessing such cards by computer in modifying the electronic circuitry of these cards as little as possible and, more specifically, in keeping standard cards. The protection system thus costs as little as possible.